In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipments (UEs), communicate via a Radio Access Network (RAN) to one or more core networks. The RAN covers a geographical area which is divided into areas or cell areas, with each area or cell area being served by a radio network node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” or “eNodeB”. The area or cell area is a geographical area where radio coverage is provided by the access node. The radio access node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio access node.
A Universal Mobile Telecommunications System (UMTS) is a third generation telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio access nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural radio access nodes connected thereto. This type of connection is sometimes referred to as a backhaul connection. The RNCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS) have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein the radio base station nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio base stations, e.g. eNodeBs in LTE, and the core network. As such, the Radio Access Network (RAN) of an EPS has an essentially “flat” architecture comprising radio base stations connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between radio base stations, this interface being denoted the X2 interface.
There exist today many coordination schemes to improve overall system efficiency of the wireless communication network by either increasing signal strength or decreasing the interference level such as Coordinated Multi-point (CoMP). Typical coordination schemes in the purpose of increasing signal strength are for example, downlink joint transmission and uplink joint reception wherein coordinated beamforming increases the signal strength of one wireless device without introducing interference to other wireless devices. CoMP is used to send and receive data to and from a wireless device from several transmission points to ensure that an optimum performance is achieved. Typical coordination schemes in the purpose of decreasing the interference are for example dynamic point blanking and dynamic point power control, wherein the signal quality in terms of Signal to Interference plus Noise Ratio (SINR) will be improved by reducing the interference power. To obtain Downlink (DL) CoMP gain, a channel quality gain due to reduced interference is estimated and then applied when selecting transport format for the wireless device.
3GPP Release (Rel)-11 of LTE has extended a channel state reporting framework with some new tools so that wireless devices supporting Rel-11 can be configured to measure the gains from the lower interference and report it to the radio network node. These tools are enabled when configuring a certain transmission mode introduced in rel-11 called Transmission Mode 10 (TM10).
For the legacy wireless devices, the channel quality gain has to be estimated based on some other means, such as Reference Signal Received Power (RSRP) or Reference Signal Received Quality (RSRQ). RSRP and RSRQ are measured on the wireless device side and reported in a measurement report back to the radio network node. RSRP is defined as a received power of the LTE Reference Signals and RSRQ is defined as:
RSRQ=(N*RSRP)/RSSI where N is a number of resource blocks over the entire bandwidth and Received Strength Signal Indicator (RSSI) is a received power of all symbols measured over the same bandwidth. The RSSI measures the average total received power observed only in Orthogonal frequency-division multiplexing (OFDM) symbols containing reference symbols for an antenna port 0, i.e., OFDM symbol 0 & 4 in a slot, in the measurement bandwidth over N resource blocks. RSSI is the total received power of the carrier. RSSI includes the power from co-channel serving & non-serving cells, adjacent channel interference, thermal noise, etc. Total measured over 12-subcarriers including Reference Signal (RS) from serving Cell and Traffic in the serving Cell. It should be noted that RSRP may be defined as the received power of Cell specific Reference signals (CRS) of the serving cell of one resource element (RE), i.e. in the unit of [W/RE]. RSSI is calculated as the sum of all received power over the bandwidth of one Physical Resource Block (PRB), i.e. in the unit of [W/PRB].
LTE networks may operate using different CRS configurations which results in different interference characteristics. In a non-shifted CRS configuration the same time and frequency resources are used for CRS transmissions in all cells of transmission points. Hence it avoids that the CRSs interfere with data transmissions, but is also associated with a systematic Channel State Information (CSI) estimation error; especially noticeable at low traffic. In a shifted CRS configuration different cells of different transmission points transmit CRSs on resources that are shifted in frequency, thus when using the shifted CRS configuration the CRSs interfere with data transmissions but the CSI estimation error is smaller. In reality, because a limited number of CRS shifts may be configured, a mixed situation occurs where a configured CRS might collide with both CRS and data from different cells.
Existing solutions of using multiple transmission points, utilize RSRP to measure and estimate channel quality gain from lowering interference. This results in a poor estimation of the channel quality since that is not reflecting the actual operation and leads to a poor usage of radio resources in the wireless communication network limiting the performance of the wireless communication network.